I would like to add comments to my single.php file. My custom theme is "hand built" and I haven't found the proper code needed to add this functionality. Anyone have the quick and dirty on how to add such a thing?

alternatively to working with the comments.php of the default theme, there is still a basic comments.php in this location /wp-includes/theme-compat/comments.php (although it does not have comment_form() implemented).